CTFE is a commercially important compound, including for use as monomer in the production of fluoropolymers.
Various methods have been used to prepare CTFE. These methods have suffered from certain disadvantages including consumption of expensive materials, low product yield or both. For example, CTFE has been prepared by a liquid phase process comprising dechlorinating 1,1,2-trichloro-1,2,2-trifluoroethane with zinc in a solvent such as methanol or ethanol. See U.S. Pat. No. 5,124,494 and US 2017/0166501. Although CTFE can be produced using processes such as these, and potentially in good yield, applicants have come to appreciate that such processes have the disadvantages of requiring a large amount of solvent and producing a zinc chloride by-product which is troublesome and expensive to remove from the reaction product. U.S. Pat. No. 5,124,494 also mentions a method for producing CTFE by reacting R-113 with hydrogen in the presence of a copper, nickel or cobalt catalyst, but reports that such a process suffers from the disadvantages of low selectivity and large amounts of impurities.
CTFE has also been prepared by the co-pyrolysis of dichlorofluoromethane and chlorodifluoromethane. However, the production of CTFE by such a co-pyrolysis suffers from the disadvantage of producing CTFE in low yield.
CTFE has been prepared by the gas phase dechlorination of 1,1,2-trichloro-1,2,2-trifluoroethane with hydrogen in the presence of various active carbon catalysts. In the gas phase process using active carbon, a space velocity cannot be larger than about 500 hr−1 resulting in low productivity. A gas phase dechlorination using a Pd catalyst has been suggested, but Pd is expensive and deactivated in a short reaction time, and the reaction carried out at a contact time of 10 to 60 seconds, so that the productivity is low. Also, the yield of CTFE was unsatisfactory.
CTFE was prepared according to a gas phase dechlorination process in U.S. Pat. No. 4,155,941. The main disadvantages of this process are reduced conversion of the starting material, low yield of the CTFE product and/or the formation of undesired material (CF2═CCl2) in significant amount (>70% in some cases with Al2O3/FeCl3 catalyst).
There is a continuing need in the art for further improvements in processes for the production of CTFE. The present invention process produces CTFE in excellent selectivity, acceptable conversion, desirably low amounts of organic by-products and easily separated inorganic by-products.